Protective circuit for enameling furnaces



April 1933- R. D. VAN NORDSTRAND 1,904,580

PROTECTIVE CIRCUIT FOR ENAMELING FURNACES Filed Jul 24, 1951 Fig].

I ww n 1% w 3? nN W S Q i m H D Lu w @W R Patented Apr. 18, 1933 UNITEDSTATES PATENT OFFICE ROBERT D. VAN NORDSTRAN D, OF SCOTIA, NEW YORK,ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORKPROTECTIVE CIRCUIT FOR ENAMELING FURNACES Application filed July 24,1931. Serial No. 553,016.

My invention relates to furnaces of the conveyor type and moreparticularly to protective means therefor and has for an object theprovision of a simple and, reliable means for deenergizing the furnaceand stopping the convevor on the occurrence of an abnormal condition,such as the dislodgement of the work from the conveyor cradles or theundue oscillation of the cradles.

In continuous vitreous enameling furnaces the furnace is usuallyconstructed with a relatively long approach chamber, and an endlessconveyor mounted on a suitable track carries the work through theapproach chamher to and from the furnace, baking the enamel on the work.

In order to maintain the coating of enamel relatively intact, the workto be enameled is usually supported on each conveyor cradle by sharppointed pins or it may be vsuspended from the cradle by suitable hooks.Inasmuch as each cradle is pivotally carried by the conveyor, anyjerkiness in the travel of the conveyor will cause thecradles tooscillate about their pivots often dislodging the work from itsrelatively unstable support. The oscillations may be great enough attimes to cause the cradle to strike the walls of the approach chamber orthe heating units within the furnace. Upon the occurrence of eithercondition, a jam may be formed, causing considerable damage.

In carrying out my invention in one form, I provide a relay forcontrolling the deene'rgization of the furnace and of the conveyordriving motor on the occurrence of an abnormal oscillation of a conveyorcradle. The relay is operated by the completion of its energizingcircuit by a cradle oscillating sufficiently for the work carriedthereon or for the cradle itself to strike a conductor extending alongthe conveyor and in juxtaposition therewith. It will thus be observedthat if either the cradle or the work carried by the cradle comes intocontact with the conductor the relay operates to deenergize the furnaceand the conveyor motor. Ordinarily, of course, the enamel is a goodinsulator but I have found that in its heated condition it issufficiently conductive to operate the relay.

It'is to be understood that my invention is not limited to the conductorarrangement described as other means will now suggest themselves whichwill respond to the oscillation of the cradles caused by the jerkyinotion of the conveyor.

For a more complete understanding of my invention reference should nowbe had to the drawing in which Figure 1 is anelevation partly in sectionof a furnace and the protectiv-e circuit therefor embodying myinvention, and Figure 2 is an elevation of one of the cradles of theconveyor loaded with work to be enameled.

Referring to the drawing, I have shown my invention in one form asapplied to a vertical vitreous enameling furnace 10 having a relativelylong approach chamber 11 within which is suitably mounted a motor drivenoverhead endless conveyor 12 as bytheconveyor track 13 secured to thewalls of the furnace. Cradles 14 are pivotally carried by the conveyor12 and are free to oscillate about their pivots 15, which aresubstantially horizontal. Each cradle as is shown in Figure 2 has aplurality of shelves as indicated by the reference numerals 16, 17 and18 and extending upwardly from each shelf there are provided a pluralityof sharp pointed pins 19 for supporting the work. It will, of course, beunderstood that the sharp pointed pins 19 provide a minimum supportingarea for each article to be enameled. There is also provided on eachcradle suitable hooks 20 from which work to be enameled such as cups orsmall utensils may be suspended.

In the operation of the conveyor 12, I have found that the cradles aresubjected to oscillations which oscillations are primarily due to ajerky motion of the conveyor arising from irregularities in the track13, or from the inherent variable friction usually encountered withrelatively long conveyors. At times the oscillations may be great enoughto dislodge the work or to cause a cradle 14 to strike the walls of theapproach chamber or of the heating coils provided within the workingchamber of the furnace 10. henever a cradle does strike the wall of thefurin nearly all cases dislodges the work from its relatively unstablesupport. And it will at once be seen that if work being enameled, suchas a bucket or the like, falls from one of the upper cradles theprobability of its striking other cradles as it falls and dislodgingmore work being enameled is very great. The result is generally a i amformed by the piling up of the utensils or articles within the furnace.The conveyor 12 not only should be immediately stopped but also theheating means for the furnace 10 should be immediately renderedineffective in order to minimize the scorching or burning of the work onthe cradles which work would otherwise be ruined.

In the form of my invention shown the heat for the furnace is generatedby the heating resistors 22, 23 and 24, which resistors are directlyconnected across the secondary 25 of a Y-connected transformer 26, theprimary 27 of which is connected through an electromagnetically operatedswitch 28 shown in its closed position to a suitable source of supplyindicated by the reference numeral 29. The energization of the motor 30driving the conveyor 12 is controlled by a switch 31 operated with theswitch 28. A suitable trip 32 is arranged .to open the switches 28 and31 whenever the trip operating coil 33 is energized, which coil 33 isarranged to be energized whenever the abnormal oscillation of a cradleoccurs, thus deenergizing the furnace heating resistors 22, 23 and 24and the conveyor motor 30.

This is accomplished by providing protective conductors 34 and 35,arranged in juxtaposition with the conveyor 12 in the approach chamberso that if a cradle in the approach chamber oscillates more than apredetermined amount either the cradle or the work carried thereon willstrike conductor 34 or conductor 35, before striking the wall of theapproach chamber, thereby energizing a relay 36 which completes thecircuit to the trip coil 33. In the furnace proper or in the workingchamber the heating resistors 22, 23 and 24 serve not only to generatethe heat for the furnace but also to perform the function of theprotective conductors 34 and 35.

It will now be assumed that the upper right hand cradle on the conveyorhas been oscillated until it strikes the heating resistor 23. Theconveyor is immediately stopped and the furnace deenergized as abovedescribed by the completion of the circuit of the relay 36 which circuitmay be traced from a transformer coil 37 by conductor 38 to the resistor24, resistor 23, the cradle in contact with resistor 23, the conveyortrack 13, by conductor 39, the operating coil of the relay 36, byconductor 40 to the neutral point of the sec-- ondary 25 of transformer26. The relay 36 now closes, establishing an energizing circuit for thetrip coil 33 which circuit may be traced from the supply line 41, relay36, trip coil 33, and to the other supply line 29. The trip 32 forswitches 28 and 31 is thereupon operated, the said switches immediatelyopening to deenergize both the conveyor motor 30 and the heatingresistors 22, 23 and 24.

Also if one of the articles being enameled strikes either the protectiveconductors 34, 35, or the heating resistors 22, 23, 24, the circuits arecompleted as above described to deenergize the furnace and the conveyormotor 30, inasmuch as the enamel becomes conductive when hot.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made, and I therefore contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. In a protective system for furnaces, the combination of heating meansfor said furnace, motor driven means for conducting work through saidfurnace along a restrict ed path, and means responsive to apredetermined departure of said motor driven means from said restrictedpath at any point thereof for rendering said heating means ineffectiveand for stopping said motor driven means.

2. The combination in a furnace of heating means for said furnace, aconveyor extending within said furnace and having work carrying cradlespivotally mounted on said conveyor, driving means for said conve or, andmeans responsive to undue oscillations of any one of said cradles withinsaid furnace for rendering said heating means ineffective and forstopping said driving means.

3. In a protective system for vitreous enameling furnaces having anapproach chamber, the combination of heating resistors for said furnace,a conveyor extending within said furnace, work carrying cradlespivotally mounted on said conveyor, a driv ing motor for said conveyor,deenergizing means for said resistors and said driving motor, andconductive means responsive to undue oscillations of any one of saidcradles about their pivots and in juxtaposition with said conveyor foroperating said deenergizing means whereby said heating resistors andsaid motor are deenergized on the occurrence of more than apredetermined oscillation of any one of said cradles.

4. In a protective system for vitreous enameling furnaces having anapproach chamber, the combination with heating resistors for saidfurnace, a conveyor, :1 plurality of work carrying cradles pivotallymounted thereon, a motor for driving said conveyor, a relay arranged todeenergize said resistors and said motor, a conductor between saidconveyor and said furnace wall arranged to be engaged by said cradleswhen unduly oscillating about their pivots, and means responsive to theengagement of a cradle with said conductor for energizing said relaywhereby said resistors and said motors are deenergized.

5. Protective means for vitreous enameling furnaces having an approachand a working chamber, a conveyor having work carrying cradles pivotallymounted thereon, a motor for driving said conveyor, a relay arranged todeenergize said motor, an energizing circuit therefor, and meansresponsive to undue oscillations of any one of said cradles in eithersaid approach chamber or said working chamber for completing saidcircuit whereby said motor is deenergized.

6. In a protective system for furnaces the combination of heatingresistors for said furnace, a conveyor for said furnace having cradlespivotally mounted thereon, a motor for driving said conveyor, meansresponsive to the contact of any one of said cradles with said resistorsfor deenergizing said resistors and said motor.

7. In a protective system for a furnace, the combination of a drivenconveyor extending therein, a driving motor for said conveyor, workcarrying means carried by said conveyor, means for stopping said drivingmotor, and means interposed between said conveyor and extending alongthe entire length of said furnace wall adjacent said conveyor toeffectuate operation of said motor stoppingmeans whenever said workcarrying means or work carried thereby strikes said interposed means.

8. In a protective system for furnaces having walls arranged to form aworking chamher and an approach chamber, the combination with heatingresistors mounted in spaced relation with the walls of said workingchamher, an endless conveyor extending through said approach chamber andinto said working chamber, a plurality of charge supporting cradlespivotally mounted on said conveyor, a motor for driving said conveyor, arelay for controlling the deenergization of said resistors and saidmotor, elongated conductors connected to said resistors and sup portedbetween said conveyor and said walls and in juxtaposition with saidconveyor, an energizing circuit for said relay completed by engagementof any one of said cradles with any portion of said conductors orresistors.

In witness whereof, I have hereunto set my hand.

ROBERT D. VAN NO'RDSTRAND.

